This invention relates to a hydraulic circuit arrangement comprising a plurality of actuators connected parallel to each other and to the high pressure line coming from the main variable displacement pump provided with a regulator for controlling a discharge rate with holding a pressure constant.
In general, the hydraulic circuit of such a construction (for simplify an expression "a parallel multiple circuit" is used hereinafter) is known as "Ring Main System" and is applied in particular, for the operation circuit of the hydraulic machinery for marine use and the like, and it is well known that the parallel multiple circuit largely contributes to integration of the oil hydraulic source and simplification of the pipe line arrangement.
FIG. 1 shows an example of the pipe line system according to the prior art to be applied for the parallel multiple circuit as above described in which the main variable displacement pump 1 is equipped with a regulator 2 for controlling the discharge rate with holding the pressure in constant. Said regulator 2 is provided with a pilot chamber 3 and serves to control the discharge rate of the main pump 1 depending on the balancing between the pilot pressure induced into the pilot chamber 3 through the pipe line 4 and the force of the spring 5. The oil delivered from the main pump 1 is led to a multiplicity of actuators 7, through the high pressure line 6 and the oil discharged from the actuators is returned to the tank 9 through the discharged oil return line 8. A sequence valve 10 is connected with its inlet port to the high pressure line 6 and with its outlet port to a reservoir or through a throttle 11. The pilot chamber 3 of the regulator 2 is connected with a line provided between the sequence valve 10 and the reservoir.
The actuators 7 to be connected to the parallel multiple circuit are normally so arranged that they work independently as long as the maximum capacity of the main pump 1 will permit and thus for such characteristics, the parallel multiple circuit arrangement is highly evaluated. Depending on the purposes of application of the actuators, however, there are such cases where the above advantageous characteristics of the parallel multiple circuit cannot be fully expected so long as it works in connection with the conventional devices. For instance, in case that the circuit is applied for an operation of the deck machinery for marine use, the actuators correspond respectively to windlasses and or mooring winches. And in such a ship mooring system, the time of the respective machines or apparatuses required for "stand-by" takes long and in many cases such "stand-by" time is rather longer than that for "operation". That is, the main pump 1 continues running even for "stand-by" time, in which case the pilot pressure working against the pilot chamber 3 of the regulator 2 through the sequence valve 10 may control the delivery of the main pump 1 to minimum while the delivery pressure transmitted to the high pressure line 6 may be maintained at a high pressure to be regulated by the sequence valve 10. In this way, even when the actuators 7 are not in an "operative" condition at all, the high pressure line 6 and the relative system are at all times kept at highly pressurized conditions, whereby such undesirable problems may be caused as noise, vibration and reduced life time of the main pump. This problem will be likely developed to such a serious one which cannot be left unsolved in particular when the parallel multiple circuit will be applied for such a mooring system as above described having a longer "stand-by" time.
Furthermore, should the actuators be required of being operated at over-loaded condition, i.e., should higher pressure be required for the high pressure line 6 than the pressure to be regulated by the sequence valve 10, there are such cases in which the delivery pressure of the main pump cannot meet the required high pressure.
FIG. 2 shows an example of the countermeasure in the past taken on the parallelly multiple circuit to avoid the above-mentioned problems, wherein the sequence valve 12 set at lower pressure is provided in addition to and in parallel with the sequence valve 10 and manual directional control valve 13 is provided for changing over flow directions between the sequence valves 10 and 12. Namely, while the actuators are at "stand-by", the directional control valve 13 is positioned as illustrated, the pipe line of the sequence valve 10 is shut and subsequently by reducing the delivery pressure of the main pump 1 to the lower pressure level to be regulated by the sequence valve 12 and by manually changing the directional control valve 13 at the time when the actuators are at "operative" condition, the delivery pressure of the main pump 1 may be brought to a high pressure condition to be regulated by the sequence valve 10. In this manner, the problems in maintaining the high pressure with the device shown in FIG. 1 at the time of "stand-by" may be managed in any way to be solved, while, however, it will be much complicated and difficult in practical operation of the mooring system to manually change over the directional control valve 13, depending on the multiplicy of the actuators being either in "operative" or "stand-by" conditions.